1. Field of the Invention
The present invention relates to an optical system vibro-isolating apparatus for preventing vibrations of an optical system in, e.g., a camera.
2. Description of the Related Art
Various conventional vibro-isolating apparatuses for optical systems in, e.g., cameras have been proposed. In a typical conventional optical system vibro-isolating apparatus, a vibration of an optical system is detected by a sensor, and an actuator is operated in accordance with an output from this sensor to rotate an optical system such as a photographic lens system, thereby canceling the vibration of the optical system.
In such an optical system vibro-isolating apparatus, accurate tracking servo must be performed to follow the vibration of the optical system. A conventional optical system vibro-isolating apparatus cannot provide an accurate tracking servo operation due to the following reasons.
That is, an operation of the vibro-isolating apparatus is delayed with respect to the vibration of the optical system and is influenced by a pivotal start position of the optical system.
The types of tracking delay of the vibro-isolating operation are a tracking delay at the start of vibro-isolating operation and a tracking delay except for this.
The tracking delay at the start of vibro-isolating operation will be described first. At the start of vibro-isolating operation, the speed of the actuator must be increased from zero speed to a speed corresponding to the vibration speed at the corresponding moment. If the actuator is started at a maximum speed of the vibration, the actuator is changed from a state of zero speed to a state of maximum speed, causing a large ringing behavior. It takes much time to converge this ringing, and a large time delay occurs until an accurate vibro-isolating operation is completed.
The delay occurring except for the start of vibro-isolating operation will be described below. The actuator comprises a reversible motor, and its rotational direction and speed are controlled by a control circuit to coincide with those of the optical system vibration detected by the sensor. In this case, the control circuit includes a clock generator for generating a clock signal having a predetermined frequency. A control state of the motor is changed in response to a clock signal input. The frequency of this clock signal is predetermined in accordance with the magnitude of an acceleration of the vibration of the optical system which is vibro-isolated by the vibro-isolating apparatus. When the clock frequency is constant, no problem occurs under the condition that the acceleration of the vibration of the optical system is constant or small. However, the acceleration is greatly changed in the vibration of a camera. When the clock frequency is determined in correspondence with a small acceleration, a change in speed of the motor cannot follow a change in speed (i.e., acceleration) of the vibration. To the contrary, when the clock frequency is determined in correspondence with a large acceleration, a change in speed of the motor is excessively large upon a decrease in acceleration. In this case, a motor speed signal has an oscillating waveform, and the motor itself generates cluttering noise. In a conventional arrangement, the clock frequency is set to be an intermediate value between maximum and minimum expected accelerations. Therefore, this clock frequency cannot cope with an acceleration close to the maximum acceleration.
Finally, an influence of the pivotal start position of the optical system will be described below. The actuator drives a rotating means for rotating the optical system. A stop position of this rotating means at the end of vibro-isolating operation, i.e., a stop position of the optical system, is not constant. On the other hand, the pivotal range of the optical system is limited. At the end of vibro-isolating operation, the optical system may be stopped at the end of this pivotal range. In this case, the next vibro-isolating operation is started from this end position, and the optical system cannot be moved in the direction of this pivotal end. Therefore, it is impossible to eliminate the vibration in this direction.